1. Field of the Invention
The present invention relates to a communication method for a mesh network system. The mesh network includes a plurality of communication terminals disposed in a mesh configuration such that adjacent communication terminals can perform data communication with each other by establishing an adjacent relationship for data communication. The present invention also relates to such mesh network system and a communication terminal used in the mesh network system.
2. Description of the Related Art
A mesh network is a communication network connected in a mesh so that communication terminals communicate with each other. An individual communication terminal, that participates in the mesh network, can communicate with other communication terminals within its communicable range (adjacent terminals). When this communication terminal wants to communicate with a remote communication terminal beyond its communicable range, multi-hop communication is performed, i.e., intermediate communication terminals between the data-sending terminal (sender) and data-receiving terminal (recipient) relay the data using a so called “bucket brigade system.” In this way, in the case of a mesh network, an individual communication terminal participating in the mesh network is only required to communicate with adjacent terminals in the same network, and therefore requires only reduced output for data communication. Even if a communication terminal between the data-sending terminal and the data-receiving terminal is damaged or removed, an alternate path can be easily secured, and failure can be more easily handled compared with such a conventional network as a start network, in which communication is disabled if a communication terminal at the center fails.
A problem of a mesh network concerns the authentication of communication terminals to participate in the network, and sharing a key. A communication terminal to participate in a network must be authenticated and communication content must be protected by a key since there is concern that the communication data may be intercepted or altered, or data may be illegally accessed or a relay transfer may be rejected. In order to eliminate such possibilities, each communication terminal, to participate, authenticates at least the adjacent communication terminals and shares a key so that each communication terminal establishes a safe adjacent relationship in which communication is not allowed with communication terminals which are not registered as an adjacent terminal.
According to a known technology to establish such a safe adjacent relationship, a communication terminal which participates in a network repeats authentication and shares a key for each adjacent communication terminal. For example, Japanese Patent Application Kokai (Laid-Open) No. 2005-278044 discloses a method used in an ad hoc network, wherein a wireless communication terminal, which relays data, sends a common key to another wireless communication terminal within the transmission range. If the wireless communication terminal which has received the common key relays the data, this common key is transferred to a next wireless communication terminal.